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Directional Control for a Buoyancy Tank

IP.com Disclosure Number: IPCOM000233991D
Publication Date: 2014-Jan-06
Document File: 5 page(s) / 1M

Publishing Venue

The IP.com Prior Art Database

Abstract

A typical buoyancy tank (BT) has an axi-symmetric circular cylinder shape which travels vertically when released. Accidental release of a BT can result in significant impacts on the assets at the sea level as well as the collapse of the existing underwater system including riser/umbilical and subsea equipment. The main function of BT is to provide a required upward force (i.e. buoyancy force) which can result in a significant upward speed and large uncertain unsafe zone due to uncontrolled directionality and BT trajectories. To prevent damages on the assets, a fin attached, at a specified position and orientation, at the side shell of the BT is proposed. A fin is any shape of objects, which creates lift and drag forces that result in deflection of BT’s trajectories and minimization of impact load through the reduced speed of the BT when released.

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Directional Control for a Buoyancy Tank

Abstract:

A typical buoyancy tank (BT) has an axi-symmetric circular cylinder shape which travels vertically when released. Accidental release of a BT can result in significant impacts on the assets at the sea level as well as the collapse of the existing underwater system including riser/umbilical and subsea equipment. The main function of BT is to provide a required upward force (i.e. buoyancy force) which can result in a significant upward speed and large uncertain unsafe zone due to uncontrolled directionality and BT trajectories. To prevent damages on the assets, a fin attached, at a specified position and orientation, at the side shell of the BT is proposed. A fin is any shape of objects, which creates lift and drag forces that result in deflection of BT’s trajectories and minimization of impact load through the reduced speed of the BT when released.

Problem: 

As an example of potential risk associated with a buoyancy tank (BT), there are nearly 19 SHRs (Single Hybrid Risers) in service, and the majority are in West Africa in deep water. The SHR has a BT that is connected by a tether chain to the riser top assembly. The main functions of BT include reduction of riser loads on the production platform and decoupling of riser motion responses from the dynamic platform motion. To provide a required upward force to the lower riser system, the SHR necessarily requires a high buoyancy capacity for the BT. This results in a significant load along the chain tether that connects the lower riser system to the BT.

Recently, the offshore oil and gas industry has witnessed a failure of the tether prior to project start up resulting in significant financial and schedule impact on the project. The result has also been a change in the regulatory requirements to avoid potential damage to assets.

A BT release due to a tether failure can have the following major impacts on the assets at the sea level as well as the collapse of the riser system:

•                    Damage on the production platform;

•                    Damage on the ocean-going vessel oil/gas offloading system; and

•                    Undesired location for the watch circle of the potential risk area.

 

Description of the Invention:

The invention is an external fin that is attached to the shell of the BT and is designed to deflect the trajectory of the BT on accidental release due to a tether failure. The key ideas are:

•                    increase eccentric drag force to induce turning moment resulting in controlled trajectory change.

•                    maximize projected area to minimize surfacing velocity of BT.

•                    add a fin that could be any shape or device that modifies the hydrodynamic forces on the BT.

The major incentives of the invention are:

•                    moving the unsafe zone of the potential impact area on the sea surface out of the asset.

•                    minimizing the risk of damages on the production platform, ocean going vessels, and infrastructure on the sea surface.

•                    improving marine op safety in installation and operation....